tive gloves should be worn over the rubber dry box gloves to provide additional protection. Other safety devices that allow remote manipulation should be used with the gloves. Detonation of explosives from static sparks can be a considerable problem in dry boxes, so adequate grounding is essential, and an antistatic gun is recommended.
Armored hoods or barricades made with thick (1.0 inch) polyvinylbutyral resin shielding and heavy metal walls give complete protection against detonations not in excess of the acceptable 20-g limit. These hoods are designed to contain a 100-g explosion, but an arbitrary 20-g limit is usually set because of the noise level in the event of a detonation. Such hoods should be equipped with mechanical hands that enable the operator to manipulate equipment and handle adduct containers remotely. A sign, such as
CAUTION: NO ONE MAY ENTER AN ARMORED HOOD FOR ANY REASON DURING THE COURSE OF A HAZARDOUS OPERATION
should be posted.
Miscellaneous protective devices such as both long-and short-handled tongs for holding or manipulating hazardous items at a safe distance and remote control equipment (e.g., mechanical arms, stopcock turners, labjack turners, remote cable controllers, and closed-circuit television monitors) should be available as required to prevent exposure of any part of the body to injury.
Potentially reactive materials must be evaluated for their possible explosive characteristics by consulting the literature and considering their molecular structures. The presence of functional groups or compounds listed in sections 5.C.9 or 5.G.6 indicates a possible explosion hazard. New compounds can be screened for explosiveness by cautious heating and hammering of very small samples. Highly reactive chemicals should be segregated from materials that might interact with them to create a risk of explosion. Highly reactive chemicals should not be used past their expiration date.
When a possibly hazardous reaction is attempted, small quantities of reactants should be used. When handling highly reactive chemicals, it is advisable to use the smallest quantities needed for the experiment. In conventional explosives laboratories, no more than 0.1 g of product should be prepared in a single run. During the actual reaction period, no more than 0.5 g of reactants should be present in the reaction vessel. This means that the diluent, the substrate, and the energetic reactant must all be considered when determining the total explosive power of the reaction mixture. Special formal risk assessments should be established to examine operational and safety problems involved in scaling up a reaction in which an explosive substance is used or could be generated.
The most common heating devices are heating tapes and mantles and sand, water, steam, wax, silicone oil, and air (or nitrogen) baths. These should be used in such a way that if an explosion were to occur the heating medium would be contained. Heating baths should consist of nonflammable materials. All controls for heating and stirring equipment should be operable from outside the shielded area. (See Chapter 6, section 6.C.5, for further information.)
Vacuum pumps should carry tags indicating the date of the most recent oil change. Oil should be changed once a month, or sooner if it is known that the oil has been exposed to reactive gases. All pumps should either be vented into a hood or trapped. Vent lines may be Tygon, rubber, or copper. If Tygon or rubber lines are used, they should be supported so that they do not sag, causing a trap for condensed liquids. (See Chapter 6, section 6.C.2, for details.)
When potentially explosive materials are being handled, the area should be posted with a sign such as
WARNING: VACATE THE AREA AT THE FIRST INDICATION OF [the indicator for the specific case]. STAY OUT. CALL [responsible person] AT [phone number].
When condensing explosive gases, the temperature of the bath and the effect on the reactant gas of the condensing material selected must be determined experimentally (see Chapter 6, section 6.D). Very small quantities should be used because detonations may occur. A taped and shielded Dewar flask should always be used when condensing reactants. Maximum quantity limits should be observed. A dry ice solvent bath is not recommended for reactive gases; liquid nitrogen is recommended. (See also Chapter 3, section 3.D.3.1.)
Organic peroxides are a special class of compounds whose unusually low stability makes them among the